1. Field of the Invention
This invention relates to a stabilized phenol red indicator composition capable of providing visual pH measurements of water in the presence or absence of a halogen.
2. Description of Prior Art
The acid-base indicator phenol red undergoes a color change in the pH range of 6.4 to 8.0 and is commonly used to measure the pH of swimming pool water. See Vogel, Textbook of Quantitive Inorganic Analysis 4th Ed., 240-43. However, in the presence of bromine (Br.sub.2), hypobromous acid or the hypobromite ion, especially higher levels, phenol red undergoes bromination (as shown in reaction I) ##STR1## to form bromophenol blue, an acid-base indicator which undergoes color change in the pH range of 3.2-4.6. In fact, the reaction of bromine with phenol red is employed as a method to determine bromide ion in water. See Method 405, Standard Methods for the Examination of Water and Wastewater, 15th Ed., p. 261. The complete conversion of phenol red to bromophenol blue makes measurement of the pH of a swimming pool impossible, while incomplete conversion of phenol red to bromophenol blue sharply reduces the usefulness of phenol red since pH measurements are erratic and inaccurate.
It is known to those practicing the art that phenol red indicator solutions are marketed containing sodium thiosulfate which is intended to function as a free halogen scavenger. This intended solution to the problem of the bromination conversion of phenol red to bromophenol blue is unsatisfactory in practice for the following reasons:
(1) incomplete and inconsistent protection against the bromination conversion of phenol red to bromophenol blue in the presence of free bromine, PA1 (2) inability to accurately measure pH in the presence of high free bromine residuals (higher than 15 ppm Br.sub.2), PA1 (3) formation of reaction products that affect the pH measurement, even at lower free bromine residuals. PA1 C. Long-term shelf life stability, PA1 phenol red, preferably in an amount greater than about 0 to about 2 weight percent of the composition; PA1 phenol, preferably greater than about 0 to about 10 weight percent; PA1 sodium hydroxide, preferably about 0 to 1 weight percent; PA1 citric acid, preferably about 0 to about 1 weight percent; and PA1 deionized water, preferably about 88 to 99 weight percent.
Improper treatment of pool water due to an inaccurate pH reading may cause damage to the pool and equipment or reduce the effectiveness of the water sanitizer. If the pH falls below the recommended range, damage to the pool and equipment may result. Concrete etching, vinyl liner damage, and corrosion of metal parts are possible in low pH water. If pH rises above the recommended range, the effectiveness of the water sanitizer is reduced because of its conversion to the less effective hypohalite ion. Both high and low pH cause bather discomfort.
Although many compounds react with halogen in the aqueous system of concern, a compound of practical utility must permit the formulation of an indicator solution with the following characteristics:
A. Complete solubility in water and freedom from color, both as formulated and after reaction with bromine,
B. The ability, when used, to reduce the free bromine residual rapidly and completely without appreciable alteration of the system's pH,
D. The ability, when used, to indicate pH accurately as compared, for example, to the results obtained with a well-calibrated pH meter,
E. The ability, when used, to adapt directly for use with a commercially available pH test block comparator, such as that used with the Taylor Chemicals, Inc. Test Kit No. 2100.
Accordingly, it is the principal object of the present invention to provide a simple and inexpensive composition which, in the presence of water containing or not containing a halogen, will provide an accurate, visual pH measurement.
It is a further object of the present invention to provide a pH-measuring composition having a shelf stability of at least one year.